I use the very out-dated Gmail Notifier client. I know it hasn’t been updated since 3 years ago but very sadly it’s still the best Gmail client around (it’s lightweight, works properly and official).
Today I finally solved one annoyance I have with this application, is that it keeps popping out the password dialog box every time I login. Until stumbled upon the solution:
If you want Gmail Notifier to do NOT ask for password each time it starts, the next time that windows pops up asking for username and password, do not use it: just close it. The Gmail Notifier icon will get an (!) warnning after that. Just open Internet Explorer and go to http://mail.Google.Com/ and login with your mail and password, and choose to keep the session open. Then go to Gmail Notifier, yet with the (!) and with the right mouse button choose the option Check Mail Now.
It will not ask you again the password with a desktop window.
Oh well, so the answer turned out to be IE, lol! It looks like the Gmail Notifier client uses IE’s component to access the server, so the password session stored in IE can be used directly. Hooraay!